416 O. C. Marsh—American Jurassic Dinosaurs. 
the pelves of some existing birds (for example Geococeyx), and 
- of a few other reptiles, it will become still more evident that 
the bone called ‘‘ pubis” in a bird, is a different bone from the 
pubis of a crocodile. The ischium in Zaosaurus is a slender 
bone, extending backward parallel with the post-pubic. It has 
a distinct obturator process, which laps over the latter bone. 
The limb bones in this genus have a distinct medullary 
cavity. The femur has a prominent great: trochanter, the 
extremity of which is separated from the neck by a fissure. 
The third trochanter is long, and curved outward. The tibia 
slightly exceeds the femur in length, the proportions in Lao- 
saurus altus being 393 to 360™" (Plate IX, figure 3). The 
fibula is slender, and the distal smaller than the proximal end. 
The astragalus is distinct from the tibia, and the caleaneum 
supports the fibula. There are but two tarsals in the second 
ro 
pointed. (Plate IX, figure 3.) 
The remains of this genus at present known are all from the 
Atlantosaurus beds of Colorado and Wyoming. Those here 
described were found in Wyoming by Mr. S. W. Williston. 
They represent an animal of slender proportions, and about 
ten feet in length. 
Yale College, New Haven, October, 1878. 
[To be continued. ] 
